Components with relatively complex three-dimensional (3D) geometries may raise difficult fabrication issues. Gas turbine engine components may have relatively complex three-dimensional (3D) geometries, including components with internal surfaces defining internal passages including internal hollow areas, internal channels, internal openings, or the like (collectively referred to herein as “internal passages”) for cooling, weight reduction, or otherwise. Additive manufacturing (AM) processes (including those which form “cores” for subsequent conventional casting) as well as other powder consolidation processes such as wrought/forgings, metal injection moldings (MIM), etc. have been developed to manufacture components having relatively complex three dimensional geometries. As used herein, the term “powder consolidation process” refers to a process in which a powdered build material is used to form an intermediate article that is used to manufacture the final component. The powdered build material is densified with bonding between adjacent atoms. Consolidation processes other than powder consolidation processes (e.g., a liquid media consolidation process, a wire feedstock consolidation process, or the like) have also been used to form an intermediate article that is used to manufacture the final component.
Intermediate articles formed from powder consolidation processes and other consolidation processes may have significant surface porosity and cracks (hereinafter “surface-connected defects”), and internal porosity and cracks (hereinafter “internal defects”). For high performance engine components that operate at high stresses and in high temperature environments, and that must endure hot flow path gases and may endure high turbine rotational speeds (e.g., in the case of rotating turbine engine components), such surface-connected and internal defects (collectively referred to herein as “defects”) are unacceptable as the structural integrity, cosmetic appearance, functionality, and mechanical properties (i.e., the “metallurgical quality”) of the component manufactured from such intermediate article may be compromised.
Conventional encapsulation and subsequent hot isostatic pressing (HIP) processing of nickel- and cobalt-based superalloy articles formed by additive-manufacturing processes have resulted in components with reduced defects, but the manufacture of substantially defect-free titanium aluminide components from articles formed by additive-manufacturing processes and other consolidation processes still needs improvement. As used herein, the term “substantially defect-free” refers to a titanium aluminide component in which greater than 95% of the defects (both surface-connected and internal defects) present in the intermediate article have been eliminated.
In general, titanium aluminide alloys are lightweight when compared to nickel-based superalloys which have approximately twice the density of titanium aluminide. Titanium aluminide alloys can maintain their structural integrity (excellent creep (time to 0.5% strain) properties (930 hours @ 40 ksi for Howmet Ti-47Al-2Nb-1Mn-0.5W-0.5Mo-0.2Si (W—Mo—Si Alloy or WMS-Cast+HIP+HTT 1850° F.) during high temperatures (up to about 900° C. for Ti-43.5Al-4Nb-1Mo-0.1B (TNMB1)), and are therefore particularly desirable for manufacturing high performance components, such as turbine engine components. The use of titanium aluminide alloy as a superalloy replacement in manufacturing turbine engine components can significantly reduce engine weight, resulting in significant fuel savings and other benefits. However, titanium aluminide alloys have generally proved difficult to process, have limited heat treatability, and generally have low ductility (2%) when compared to Inconel 718 (3%) at room temperature (about 25 to about 35° C.). For example, the relatively low ductility of titanium aluminide alloys as compared with nickel- and cobalt-based superalloys combined with the very nature of a powder consolidation process in which titanium aluminide powders may be sintered (fused) to form the article results in significant cracking and porosity that are not sufficiently reduced by conventional encapsulation and HIP processing.
Accordingly, it is desirable to provide substantially defect-free titanium aluminide components and methods for manufacturing the same from articles formed by consolidation processes. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.